The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Wireless local area network (WLAN) technology has evolved rapidly over the past decade. Development of WLAN standards such as the Institute for Electrical and Electronics Engineers (IEEE) 802.11a, 802.11b, 802.11g, and 802.11n Standards has improved single-user peak data throughput. For example, the IEEE 802.11b Standard specifies a single-user peak throughput of 11 megabits per second (Mbps), the IEEE 802.11a and 802.11g Standards specify a single-user peak throughput of 54 Mbps, and the IEEE 802.11n Standard specifies a single-user peak throughput of 600 Mbps. Work has begun on a new standard, IEEE 802.11ac that will be operated in the 5 GHz bands overlapping with legacy IEEE 802.11a/n systems and with promises of throughputs exceeding 6.9 Gbps. Unlike the other standards, the IEEE 802.11ac Standard will allow simultaneous communication from an access point to multiple different client stations.
WLANs typically operate in either a unicast mode or a multicast mode. In the unicast mode, an access point (AP) transmits information to one user station at a time. In the multicast mode, the same information is transmitted to a group of client stations concurrently. With IEEE 802.ac Standard, the multicast mode is able to transmit to multiple client stations at a time.
Antennas and, accordingly, associated effective wireless channels are highly directional at frequencies near or above 60 GHz. When multiple antennas are available at a transmitter, a receiver, or both, it is therefore important to apply efficient beam patterns using the antennas to better exploit spatial selectivity of the corresponding wireless channel. Generally speaking, beamforming is a signal processing technique for using multiple transmit antennas to produce an output that combines constructively at one or more receive antennas, e.g. by producing an antenna gain pattern having one or more high gain lobes or beams (as compared to the gain obtained by an omni-directional antenna) at the receive antennas, with reduced gain in other directions. If the gain pattern for multiple transmit antennas, for example, is configured to produce a high gain lobe in the direction of a receiver, better transmission reliability can be obtained over that obtained with an omni-directional transmission.
Beamforming requires knowledge of the downstream channel between the access point and each client device. Generally, for protocols like IEEE 802.11a/b/g/n, this means that the access point will receive feedback signals indicative of the downstream channel. However, with IEEE 802.11ac, and protocols that allow for simultaneous communications with multiple client stations, the size (bandwidth) of the downstream channel can be large enough that feedback signals indicative of the entire downstream channel are difficult to produce. A high demand is placed on hardware of the responding client devices called upon to provide feedback on the entire downstream channel.